1. Field of the Disclosure
The disclosure generally relates to fuel injectors and, more particularly, to reducing or eliminating latching effects in control valves of the fuel injectors.
2. Related Art
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In conventional designs, a driver delivers a current or voltage to an open solenoid coil assembly. The magnetic force generated in the open solenoid coil assembly shifts a spool into an open position so as to align grooves or orifices (hereinafter referred to as “grooves”) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high-pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high-pressure plunger chamber. As the pressure in the high-pressure plunger chamber increases, the fuel pressure begins to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve shifts against a needle spring and opens an injection hole in a nozzle tip. The fuel is then injected into the combustion chamber of the engine.
However, in such conventional systems, over time, changes in latching effects between the spool and the solenoids coil assembly retard the injection start due to a delayed motion of the spool in the opening direction. For example, the spool may temporarily latch to the solenoid coil assembly, which delays the spool from moving. In this manner response times between the injection cycles may be slowed, thus decreasing the efficiency of the fuel injector. It has been further found that this reduced efficiency has increased at higher rail pressures. Time delays regarding first injection events at the pulse width map are also frequently observed. This reduction of the fuel quantity may also be accompanied by higher shot to shot variation. Also, fuel deterioration is potentially caused by small changes of about a 0.5 μm wear on the surfaces between the spool and the solenoid coil assemblies in combination with oil present in the solenoid coil assemblies.
Accordingly, there is a need for overcoming one or more of the problems as set forth above.